Why Future Volcanic Eruptions Could Be More Deadly Than They've Been In The Past

In June 1816, there was snowfall in New England. It was the year after the eruption of Mount Tambora in Indonesia, which released millions of tonnes of dust, ash, and sulfur dioxide into the atmosphere, casting a temporary chill across the planet. Global temperatures dropped by as much as 3 degrees and huge swathes of the northeastern United States and western Europe witnessed frost and intense, gloomy storms in June, July, and August. This earned 1816 the nickname "the year without summer".

So how did just one eruption (albeit a big one) plunge the whole world into a volcanic winter?

After the initial explosion, sulfur dioxide in the atmosphere converted to sulfate particles called aerosols. These formed a light-reflecting barrier between the Earth and the Sun, cooling the planet. Meanwhile, an increase in land mass covered in snow and ice exacerbated the cooling process.

Fortunately, the effect was temporary and the oceans helped counterbalance the cooling. When ocean surface temperatures dropped, the water particles sank. Warmer water then rose to the surface, releasing heat into the atmosphere.

A new paper published in Nature Communications suggests that if a similar eruption were to occur in the near future, it could have far more damaging and dramatic consequences because of climate change.

Scientists from the National Center for Atmospheric Research (NCAR) used computer simulations from the Community Earth System Model to work out what would happen if there was another Tambora in 2085. They found that temperatures would drop below what they did in 1816 and the water cycle would be disrupted more severely.

"We discovered that the oceans play a very large role in moderating, while also lengthening, the surface cooling induced by the 1815 eruption," NCAR scientist John Fasullo, lead author, explained in a press release. "The volcanic kick is just that – it's a cooling kick that lasts for a year or so. But the oceans change the timescale. They act to not only dampen the initial cooling but also to spread it out over several years."

It comes down to having a more stratified ocean and warmer sea surface temperatures. This prevents the warmer water on the ocean's surface from mixing with the cold, dense water below as it did in 1816. Were there to be an eruption, the colder surface water would not be able to mix with the warmer water below.

This means icier temps and more droughts.

"The response of the climate system to the 1815 eruption of Indonesia's Mount Tambora gives us a perspective on potential surprises for the future, but with the twist that our climate system may respond much differently," said co-author Otto-Bliesner.